How diversified are the forms of aquatic life! "Nature revels in these diversities," to paraphrase the saying of one of the ancient kings of France. Here are animals, the frame of which might have been designed by a geometrician. They are called Star Corals (_Astrea_). Their resemblance to the well-known figure was too striking to escape the observation of naturalists; but the organization of these creatures of the ocean is far from being rigorously regular, for Nature rarely employs perfectly straight lines, giving an evident preference to circles and waving lines. [Illustration: Fig. 70. Astrea punctifera (Lamarck).] The _Astrea_ are inhabitants of the Indian Ocean, where they are found in a great variety of forms, which has led to their subdivision into many genera by Messrs. Milne Edwards and J. Haime. The animals are short, more or less cylindrical, with rounded mouth placed in the centre of a disk, covered with a few rather short tentacula; the cells are shallow, with radiating lamellæ in _Astrea punctifera_ (Fig. 70), forming by their union a many-formed coral, which often encrusts other bodies. In short, this polyp may be described as a parasite, for it generally attaches to some other bodies, and it is by no means unusual to meet with it attached even to shells. [Illustration: Fig. 71. Meandrina cerebriformis (Lamarck).] The _Meandrina_ differ from the _Astreas_ in having the surface hollowed out into shallow sinuous elongated cells, furnished on each side of the mesial line with hooked lamellæ, ending against one or other of the ridges with separate valleys; the polypidom, which is calcareous, being fixed, simple, and inversely conical when young, and globular when old. The animals have each a distinct mouth, and lateral series of short tentacula; they are contained in shallow cells, meeting at the base, and forming by their union long and tortuous hollows. _Meandrina cerebriformis_ (Fig. 71), so called from its resemblance to the folds of the brain, is a native of the American Seas. The _Fungia_, so called by Lamarck from their resemblance to the vegetable Fungi, are too remarkable in their appearance to be passed over in silence. The major part of the species only occur in recent geological strata. Nevertheless some of the species were very numerous in the Cretaceous period, and even find representatives in the Silurian period; it is this group in which Madrepores of great size are found. [Illustration: Fig. 72. Fungia echinata (Milne Edwards).]